Method for the hydrogenation of carbonyl compounds

ABSTRACT

A carbonyl compound or a mixture of two or more carbonyl compounds is catalytically hydrogenated in the presence of a Raney copper catalyst in the form of nuggets.

This application is a 371 of PCT/EP98/04402 filed Jul. 15, 1998.

The invention relates to a process for the catalytic hydrogenation ofcarbonyl compounds in the presence of a Raney copper catalyst.

Catalytic hydrogenation of carbonyl compounds, such as the hydrogenationof aldehydes to prepare simple and functionalized alcohols, occupies animportant place in the production sequences in the basic chemicalsindustry. This is particularly true of the hydrogenation of aldehydeswhich can be obtained by the oxo synthesis or the aldol reaction.

Catalytic hydrogenation of aldehydes in a suspension or fixed bedprocedure has been known for a long time. Industrial systems operatealmost exclusively with fixed bed reactors.

The fixed bed catalysts used in particular are supported catalysts, forexample Cu/Ni or Cu/Cr catalysts supported on SiO₂ or Al₂O₃.

Suitable alternatives to the supported catalysts are Raney-typecatalysts. Raney catalysts show particularly high hydrogenation activityowing to the large surface area of metal. Suitable metals are nickel,cobalt, iron and copper.

SU 430 876 describes the hydrogenation of furfural on a Raney coppercatalyst in a suspension procedure. Suspension processes have thedisadvantage by comparison with fixed bed processes that the catalystconsumption is greater. It is furthermore necessary for the catalyst tobe removed from the reaction mixture in an additional step.

RO 106 741 describes a process for the hydrogenation of furfural tofurfuryl alcohol in a fixed bed reactor in a downflow procedure. Raneycopper inter alia is employed as catalyst. The publication contains noinformation on the preparation of the catalyst and its properties.

JP-A-3 141 235 describes a process for the hydrogenation of acetone toisopropanole wherein a Raney nickel catalyst is employed. It isdescribed that the Raney nickel catalyst is mixed with a Raney coppercatalyst. At the same time, however, it is implicitly stated that whenadding more than a certain amount of said catalyst, productivity will bedecreased.

Raney catalysts which can be used in a fixed bed process are normallyprepared by kneading an aluminum/copper alloy powder with binders andauxiliaries, producing moldings, for example tablets or extrudates, fromthe kneaded composition, calcining the moldings and activating thecalcined moldings by treatment with an alkali metal hydroxide. Processesof this type for preparing Raney catalysts are described, for example,in DE-A 43 45 265, Ind. Eng. Chem. Res. 28 (1989) 1764-1767 and DE-A 4446 907. Preparation of the catalyst by this process involves a pluralityof steps.

It is an object of the present invention to provide a process for thecatalytic hydrogenation of carbonyl compounds employing a catalyst whichis easy to prepare industrially and has high activity and selectivity.

We have found that this object is achieved by employing Raney copper inthe form of nuggets for the hydrogenation of carbonyl compounds to, forexample, the corresponding alcohols with a high catalytic activity andselectivity exceeding the activity and selectivity of Raney coppercatalysts prepared according to the prior art.

Accordingly the object has been achieved by a process for the catalytichydrogenation of a carbonyl compound or of a mixture of two or morecarbonyl compounds in the presence of a Raney copper catalyst, whereinthe Raney copper catalyst is employed in the form of nuggets.

Nuggets mean that the metal is in the form of particles of irregulargeometry with a size of from 0.5 to 10 mm. The Raney copper nuggets areproduced from coarse-particle copper/aluminum alloy, without theintermediate steps of kneading the copper/aluminum alloy with a binderand/or auxiliary, shaping the kneaded composition to moldings andcalcining the moldings, by treatment of the coarse-particlecopper/aluminum alloy with alkali metal hydroxide.

The nuggets employed in the process according to the invention can befrom 0.5 to 10 mm in size. They are preferably from 1 to 8 mm,particularly preferably from 2 to 7 mm, especially from 2 to 6 mm.

The Raney copper used in the process according to the invention isprepared starting from a copper/aluminum alloy. The copper/aluminumalloy is prepared in a manner known per se, for example by the processdescribed in DE-A 21 59 736. The ratio by weight of aluminum to copperin the initial alloy is generally chosen in the range from 30:70 to70:30% by weight, preferably from 40:60 to 60:40% by weight.

The Raney copper catalyst is prepared from the copper/aluminum alloy bydissolving out the catalytically inactive constituents with alkali metalhydroxide (activation). Preferred alkali metal hydroxides are sodiumhydroxide or potassium hydroxide, and sodium hydroxide is particularlypreferred. An aqueous solution of the alkali metal hydroxide isgenerally employed, preferably sodium or potassium hydroxide solution,particularly preferably sodium hydroxide solution, normally using a5-30% by weight aqueous solution of the alkali metal hydroxide. Themolar ratio of alkali metal hydroxide to aluminum is generally chosen inthe range from 1:1 to 4:1, preferably from 1.5:1 to 2.5:1. Theactivation is normally carried out at from 25° C. to 95° C., preferably45 to 90° C. The duration of the activation essentially depends on therequired final aluminum content and is normally in the range from 10 to30, preferably 15 to 25, h. The activation is expediently monitored bymeasuring the amount of hydrogen liberated during it. The activationprocess can also be carried out several times.

The starting material for the activation is normally the coarse-particlecopper/aluminum alloy. The size of the copper/aluminum alloy particlescan correspond to that of the Raney copper nuggets employed in theprocess according to the invention. However, it is also possible for theparticles to be reduced to the required size after the activation.

The Raney copper catalysts employed in the process according to theinvention preferably have a copper content of from 40 to 90% by weight,more preferably from 50 to 80% by weight, particularly preferably from60 to 70% by weight.

The Langmuir specific surface area of the Raney copper catalystsemployed in the process according to the invention is preferably from 5to 50 m²/g, more preferably from 15 to 40 m²/g, particularly preferablyfrom 20 to 40 m²/g. The Langmuir surface area is determined by nitrogenabsorption using the DIN 66 132 method.

A variable characteristic of the Raney copper catalysts according to theinvention is also their specific Cu surface area (S—Cu). It iscalculated from the N₂O consumption measured on oxidation of surfacecopper atoms with gaseous N₂O in a heated sample of the catalyst.

This is done by initially treating the sample with 10 mbar of H₂ at 240°C. for 4 hours. The pressure over the sample is then reduced to lessthan 10⁻³ mbar, and it is then treated with 30 mbar of H₂ for 3 hours,subsequently the pressure is again reduced to less than 10⁻³ mbar,followed by treatment with 100 mbar of H₂ for 3 hours, the pressure isagain reduced to less than 10⁻³ mbar, followed by a final treatment with200 mbar of H₂ for 3 hours, the hydrogen treatment in each case beingcarried out at 240° C.

In a second stage, the sample is exposed to N₂O under a pressure of 266mbar at 70° C. for 2 hours, the N₂O being decomposed on the sample; thepressure over the sample is then reduced to less than 10⁻³ mbar, afterwhich the increase in weight of the catalyst as a result of theformation of copper oxide on the surface thereof is determined.

The specific Cu surface area of the Raney copper catalysts is preferablyfrom 0.5 to 7 m²/g, more preferably from 1 to 4 m²/g.

The pore volume of the Raney copper catalyst determined by mercuryporosimetry is preferably from 0.01 to 0.12 ml/g, more preferably from0.03 to 0.08 ml/g. The average pore diameter determined by this methodis preferably from 50 to 300 nm, more preferably from 60 to 100 nm. Themercury pore volume and the pore diameter are determined by the DIN 66133 method.

The apparent density of the Raney copper nuggets employed in the processaccording to the invention is generally from 1.9 to 2.4, preferably from1.9 to 2.1, g/ml.

The process according to the invention can be carried out as fixed bedreaction with the catalyst in a fixed bed, or as fluidized bed reactionwith the catalyst undergoing fluidization. The fixed bed is preferablyused. The hydrogenation can be carried out in the gas phase or liquidphase. The hydrogenation is preferably carried out in the liquid phase,for example in a downflow or upflow procedure.

In a preferred embodiment of the process according to the invention witha downflow procedure, part of the product is, after passing through thereactor, continuously taken off as product stream, and the other part ofthe product is returned to the reactor together with fresh precursorcontaining the carbonyl compound. This procedure is referred to as therecycle procedure hereinafter.

In a downflow procedure, the liquid precursor containing the carbonylcompound to be hydrogenated is allowed to flow downwards over thecatalyst bed which is arranged in the reactor, which is under a highpressure of hydrogen, with formation of a thin film of liquid on thecatalyst. On the other hand, in an upflow procedure, hydrogen gas ispassed into the reactor filled with the liquid reaction mixture, inwhich case the hydrogen passes through the catalyst bed as ascending gasbubbles.

In the upflow procedure, the process according to the invention can becarried out either batchwise or continuously. The process can be carriedout continuously by taking off all the liquid product after passingthrough the reactor or else, in a similar manner to the proceduredescribed above, taking off only part of the product and returning theother part of the product together with fresh precursor containing thecarbonyl compound to the reactor (recycle procedure). The process ispreferably carried out continuously, with all of the product being takenoff after the precursor has passed once (straight) through the reactor.

The process according to the invention is suitable for the hydrogenationof carbonyl compounds such as aldehydes and ketones to give thecorresponding alcohols, with aliphatic and cycloaliphatic saturated andunsaturated carbonyl compounds being preferred. In the case of aromaticcarbonyl compounds there may be unwanted formation of byproducts due tohydrogenation of the aromatic nucleus. The carbonyl compounds may haveother functional groups such as hydroxyl or amino groups. Unsaturatedcarbonyl compounds are generally hydrogenated to the correspondingsaturated alcohols. The term “carbonyl compounds” used in connectionwith the invention includes all compounds which have a C═O group,including carboxylic acids and derivatives thereof.

The process according to the invention is preferably employed for thehydrogenation of aliphatic aldehydes, hydroxy aldehydes, ketones, acids,esters, anhydrides, lactones and sugars.

Preferred aliphatic aldehydes are branched and unbranched saturatedand/or unsaturated aliphatic C₂-C₃₀ aldehydes as can be obtained, forexample, by the oxo synthesis from linear or branched olefins with aninternal or terminal double bond.

Examples of aliphatic aldehydes are:

propionaldehyde, n-butyraldehyde, isobutyraldehyde. valeraldehyde,2-methylbutyraldehyde, 3-methylbutyraldehyde (isovaleraldhyde),2,2-dimethylpropionaldehyde (pivalaldehyde), caproaldehyde,2-methylvaleraldehyde, 3-methylvaleraldehyde, 4-methylvaleraldehyde,2-ethylbutyaldehyde, 2,2-dimethylbutyraldehyde,3,3-dimethylbutyraldehyde, caprylaldehyde and capraldehyde.

Besides the short-chain aldehydes mentioned, also particularly suitableare long-chain aliphatic aldehydes which can be obtained, for example,by oxo synthesis from linear α-olefins.

Enalization products are particularly preferred, eg. 2-ethylhexenal,2-methylpentenal, 2,4-diethyloctenal or 2,4-dimethylheptenal.

Preferred hydroxy aldehydes are C₃-C₂ hydroxy aldehydes which can beobtained, for example, by aldol reaction from aliphatic andcycloaliphatic aldehydes and ketones with themselves or formaldehyde.Examples are 3-hydroxypropanal, dimethylolethanal, trimethylolethanal(pentaerythrital), 3-hydroxybutanal (acetaldol),3-hydroxy-2-ethylhexanal (butyraldol), 3-hydroxy-2-methylpentanal(propionaldol), 2-methylolpropanal, 2,2-dimethylolpropanal,3-hydroxy-2-methylbutanal, 3-hydroxypentanal, 2-methylolbutanal,2,2-dimethylolbutanal and hydroxypivalaldehyde. Hydroxypivalaldehyde(HPA) and dimethylolbutanal (DMB) are particularly preferred.

Preferred ketones are acetone, butanone, 2-pentanone, 3-pentanone,2-hexanone, 3-hexanone, cyclohexanone, isophorone, methyl isobutylketone, mesityl oxide, aceto-phenone, propiophenone, benzophenone,benzalacetone, dibenzalacetone, benzalacetophenone, 2,3-butanedione,2,4-pentanedione, 2,5-hexanedione and methyl vinyl ketone.

It is also possible to react carboxylic acids and derivatives thereof,preferably those having 1-20 carbon atoms. The following may bementioned in particular:

Carboxylic acids such as formic acid, acetic acid, propionic acid,butyric acid, isobutyric acid, n-valeric acid, trimethylacetic acid(pivalic acid), caproic acid, enanthic acid, caprylic acid, capric acid,lauric acid, myristic acid, palmitic acid, stearic acid, acrylic acid,methacrylic acid, oleic acid, elaidic acid, linoleic acid, linolenicacid, cyclohexanecarboxylic acid, benzoic acid, phenylacetic acid,o-toluic acid, m-toluic acid, p-toluic acid, o-chlorobenzoic acid,pchlorobenzoic acid, o-nitrobenzoic acid, p-nitrobenzoic acid, salicylicacid, p-hydroxybenzoic acid, anthranilic acid, p-aminobenzoic acid,oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid,pimelic acid, suberic acid, azelaic acid, sebacic acid, maleic acid,fumaric acid, 1,4-cyclohexanedicarboxylic acid, phthalic acid,isophthalic acid and terephthalic acid;

Carbonyl halides such as the chlorides or bromides of the abovementionedcarboxylic acids, especially acetyl chloride or bromide, stearylchloride or bromide and benzoyl chloride or bromide, which undergodehalogenation in particular;

Carboxylic esters such as the C₁-C₁₀-alkyl esters of the abovementionedcarboxylic acids, in particular methyl formate, ethyl acetate, butylbutyrate, dimethyl terephthalate, dimethyl adipate, methyl(meth)acrylate, butyrolactone, caprolactone and polycarboxylic esterssuch as polyacrylic acid polymethacrylic esters and their copolymers andpolyesters, eg. poly(methyl methacrylate), carrying out in these casesin particular hydrogenolyses, ie. conversion of esters into thecorresponding acids and alcohols;

Carboxylic anhydrides such as the anhydrides of the abovementionedcarboxylic acids, in particular acetic anhydride, propionic anhydride,benzoic anhydride and maleic anhydride.

Carboxamides such as formamide, acetamide, propionamide, stearamide andterephthalarnide.

It is also possible to react hydroxy carboxylic acids such as lactic,malic, tartaric or citric acid, or amino acids such as glycine, alanine,proline and arginine.

The process according to the invention is particularly preferablyemployed for the hydrogenation of aldehydes and hydroxy aldehydes.

The carbonyl compound to be hydrogenated can be fed as gas or liquidinto the hydrogenation reactor alone or as a mixture with thehydrogenation product, and the liquid can be in undiluted form or mixedwith additional solvent. Particularly suitable additional solvents arewater, alcohols such as methanol, ethanol and the alcohol produced underthe reaction conditions. Preferred solvents are water, THF, NMP, andethers such as dimethyl and diethyl ethers, MTBE, and water isparticularly preferred.

The hydrogenation in both an upflow and a downflow procure is generallycarried out at from 50 to 250° C., preferably at 70 to 200° C.,particularly preferably at 100 to 140° C. under a pressure of from 15 to250 bar, preferably 20 to 200 bar, particularly preferably 25 to 100bar.

High conversions and selectivities are achieved with the processaccording to the invention. The catalyst employed has a higher activitythan prior art catalysts. The hydrogenation can therefore be carried outwith distinctly higher space velocities without loss of conversion andselectivity. In addition, the catalyst is simple to prepare becausesteps such as shaping and calcination are omitted. This makes theprocess according to the invention particularly economic.

The invention is explained in detail by the following examples

EXAMPLE 1

Hydrogenation of Hydroxypivalaldehyde (HPA) to Neopentyl Glycol (NPG) ina Downflow Procedure

The initial solution comprises a mixture of 38% by weight HPA and 38% byweight NPG in 24% by weight water. This mixture was hydrogenated in areactor with a length of 50 cm and an internal diameter of 4.25 cm(reactor volume 200 ml), charged with

a) 200 ml of Al₂O₃-supported copper catalyst prepared as disclosed inEP-A 0 044 444 in tablet form (3×3 mm), Cu content 36% by weight,apparent density 1090 g/l, BET surface area 101 m²/g, specific Cusurface area 11.5 m²/g as catalyst A, or

b) 200 ml of SiO₂-supported copper catalyst prepared as disclosed in WO95/32171 in bead form (diameter 3 mm), Cu content 18% by weight,apparent density 605 g/l, BET surface area 212 m²/g, specific Cu surfacearea 9.8 m²/g, as catalyst B, or

c) 200 ml of Raney copper prepared as disclosed in DE-A 44 46 907 intablet form (3×3 mm), Cu content 72% by weight, apparent density 2000g/l, Langmuir surface area 24 m²/g, specific Cu surface area 2.6 m²/g,Hg pore volume 0.06 ml/g, average pore diameter (from Hg porosimetry) 84nm, as catalyst C, or

d) 200 ml of Raney copper in the form of nuggets (diameter 3 mm), Cucontent 56% by weight, apparent density 1950 g/l, Langmuir surface area26 m²/g, specific Cu surface area 3.1 m²/g, Hg pore volume 0.07 ml/g,average pore diameter (from Hg porosimetry) 92 nm, as catalyst D(according to the invention)

at a space velocity of 0.351 HPA/l catalyst×h at 130° C. under 35 bar inthe downflow and recycle procedures (recycling 9.5 l/h).

EXAMPLE 2

Hydrogenation of 2,2-dimethylolbutanal (DMB) to 1,1,1-trimethylolpropanein an Upflow Procedure

The initial solution was a 45% by weight aqueous DMB solution. Thissolution was hydrogenated in an upflow procedure in a reactor with alength of 30 cm and an internal diameter of 2.5 cm charged with 150 mlof catalyst B, C or D (according to the invention) from Example 1 at120° C. under 90 bar. The solution was pumped straight through thereactor with various space velocities: 0.2, 0.3, 0.4 and 0.6 kg DMB/lcatalyst×h.

Table 1 summarizes the results.

The results make it clear that the highest conversions and selectivitiesare achieved with catalyst D under conditions which are otherwiseidentical.

TABLE 1 Conversion Selectivity Space (from the (from the Cata- Pre-velocity GC % GC % lyst cursor Procedure kg/l_(CAT).h areas) % areas) %A HPA downflow/ 0.35 86.8 89.1 recycle B HPA downflow/ 0.35 94 92.5recycle B DMB upflow 0.2 99.44 78.91 B DMB upflow 0.3 90.84 75.28 C HPAdownflow/ 0.35* 95.2 93.3 recycle C DMB upflow 0.2 100 89.97 C DMBupflow 0.4 97.65 87.34 C DMB upflow 0.6 88.79 74.52 D HPA downflow/ 0.3596.8 94.2 recycle D DMB upflow 0.2 100 91.17 D DMB upflow 0.4 100 90.7 DDMB upflow 0.6 95.45 87.3 *l_(HPA)/kg_(cat).h

We claim:
 1. A process for the catalytic hydrogenation of a carbonylcompound or of a mixture of two or more carbonyl compounds in thepresence of a Raney copper catalyst, wherein the Raney copper catalystis employed in the form of nuggets and wherein the nuggets are particlesof irregular geometry with a size of 0.5 to 10 mm.
 2. A process asclaimed in claim 1, wherein the Raney copper catalyst has the followingproperties: size of the nuggets from 2 to 7 mm copper content from 40 to90% by weight Langmuir surface area from 5 to 50 m²/g Cu surface areafrom 0.5 to 7 m²/g Hg pore volume from 0.01 to 0.12 ml/g average porediameter from 50 to 300 nm.
 3. A process as claimed in claim 1, whereinthe catalytic hydrogenation is carried out as fixed bed reaction in adownflow procedure.
 4. A process as claimed in claim 1, wherein thecatalytic hydrogenation is carried out as fixed bed reaction in anupflow procedure.
 5. A process as claimed in claim 3, wherein theprocess is additionally carried out in a recycle procedure.
 6. A processas claimed in claim 4, wherein the process is additionally carried outin a recycle procedure.
 7. A process as claimed in claim 3, wherein thehydrogenation is carried out at from 70 to 200° C. under a pressure offrom 20 to 200 bar.
 8. A process as claimed in claim 4, wherein thehydrogenation is carried out at from 70 to 200° C. under a pressure offrom 20 to 200 bar.
 9. A process as claim in claim 1, wherein analiphatic aldehyde or an aliphatic hydroxy aldehyde or a mixture of twoor more thereof is employed as carbonyl compound.
 10. A process asclaimed in claim 9, wherein hydroxypivalaldehyde or dimethylolbutanal isemployed as carbonyl compound.
 11. A process as claimed in claim 1,wherein water is present as solvent.